This invention relates to in-die hydropiercing apparatus with prepiercing adjustment and more particularly to the adjustable positioning and holding of the backup plunger in determining the amount of hydroprepiercing allowed prior to actual hydropiercing.
In the hydroforming of a part, it is well known that one or more holes required in a hydroformed part may be pierced in the part while the part remains in the dies by using the hydroforming pressure to effect the piercing immediately following the forming of the part with this pressure. Thereby eliminating the need to form the holes in a subsequent operation such as by drilling, plasma cutting or laser cutting after the part has been removed from the hydroforming dies. And in view of how such prepiercing and subsequent piercing is accomplished, the actual piercing is referred to herein as hydropiercing and the prepiercing that is performed prior thereto and immediately following the hydroforming of the part is referred to herein in similar manner as hydroprepiercing as both such operations are performed with the hydroforming fluid used to form the part.
Prior known hydroforming apparatus including in-die hydropiercing apparatus that is believed relevant is found in U.S. Pat. No. 5,398,533 that is assigned to the assignee of this invention. Wherein a die button is mounted in the lower die so that an outer surface of the die button forms a continuation of the die cavity surface. A backup plunger is received in the die button and a wedge shaped cam is positioned with a hydraulic cylinder or other suitable cam actuator and operates on one end of the plunger to position the plunger in (1) a hydroforming position so that the other end (the working end) of the plunger is flush with the outer surface of the die button for the hydroforming of the part, (2) a retracted piercing position in the die button allowing the hydroforming pressure in the part to pierce or shear the part with the cutting edge of the die button in a hydropiercing operation and wherein the slug resulting from such hydropiercing is deposited on the working end of the plunger immediately following the hydroforming of the part, and (3) a further retracted position outside of and behind the die button allowing ejection of the slug from the plunger and out of the lower die.
Other prior known hydroforming apparatus including in-die hydroprepiercing and hydropiercing apparatus that is also believed relevant is disclosed in U.S. patent application Ser. No. 09/997,369 filed Nov. 30, 2001 and also assigned to the assignee of this invention. In the latter hydroforming apparatus, there is no intermediary cam device and either one hydraulic cylinder or two hydraulic cylinders are used to establish the prepiercing and piercing positions of the backup plunger. Wherein as to the former plunger position, the working end of the backup plunger is positioned in a partially retracted intermediate and predetermined prepiercing position in the die button that allows the hydroforming pressure to stretch a section of the part over the cutting edge of the die button and only partially into the die button and against the outer end of the plunger. This prepiercing action, that may also be referred to as a hydropreshearing operation, weakens but does not pierce this section of the part at the cutting edge of the die button and thereby allows reduced hydroforming pressure less prone to leakage past plunger to effect the piercing when the end of the plunger is then further retracted to its piercing position. However, in this case the plunger with the slug having been deposited thereon is then returned to its hydroforming position following removal of the pierced hydroformed part from the lower die where after the slug is then ejected from the lower die with an ejection mechanism through an opening in this die""s die cavity surface.
Where such advantageous hydroprepiercing or preshearing is to be implemented in the in-die piercing of a hole with hydroforming fluid pressure, it is important that the working end of the backup member be accurately and reliably positioned in both the desired hydroforming position and the prepiercing position as otherwise the part may either not be weakened to the extent desired because of insufficient plunger retraction in the die button. Or the part may be prematurely pierced because of excessive plunger retraction in the die button.
In the aforementioned U.S. Pat. No. 5,398,533, the hydroforming position of the backup plunger is determined by the plunger having a shoulder that engages an internal stop provided on the die button and the plunger is moved to this position and eventually allowed to move to its piercing and slug ejecting positions by the hydraulic cylinder operated cam. And there is no means disclosed for adjusting the positioning of the plunger as its hydroforming position can be accurately determined by the stop and the other plunger positions; namely the piercing and slug ejecting positions, would not normally require any adjustment provided all the relevant parts are made to their required dimensions within prescribed tolerances and installed properly.
On the other hand, in the aforementioned U.S. patent application Ser. No. 09/997,369, accurate location of both the hydroforming position and the prepiercing position of the backup plunger is critical and there is disclosed therein in one embodiment mechanical means in the form of a fine threaded adjustment device for accurately adjusting the prepiercing plunger position while relying on a fixed stop at the end of a first hydraulic cylinder to accurately determine the hydroforming plunger position. The hydraulic force of a second hydraulic cylinder is required to hold both these positions in this embodiment and the adjustment device does not lend itself to providing adjustment of the prepiercing plunger position where it is desired to use the rigidity of a pure mechanical device. Rather than a hydraulic force to hold the backup plunger in its prepiercing position against the force of the high hydroforming fluid pressure in the part that can for example reach 25,000 psi. In another embodiment in the above-identified patent application, a mechanical stop provided in the die button determines the hydroforming/slug ejecting position of the plunger that is actuated by a single hydraulic cylinder. And the prepiercing position is effected by controlled partial exhaust of the hydraulic cylinder that can be adjusted to obtain the desired degree of hydroprepiercing and wherein the piercing plunger position is established by completely exhausting this hydraulic cylinder.
While the above backup plunger positioning devices have proven generally satisfactory, there remains a desire for being able in the case of prepiercing the hydroformed part to easily and finely adjust the prepiercing position of the plunger and thereby precisely control the degree of extrusion of the part into the die button without allowing actual piercing of the part at the high hydroforming pressure and without requiring the use of a hydraulic force to hold this critical plunger position. And especially when it is desired to somehow relieve a plunger positioning hydraulic cylinder of having to both establish and hold the plunger in its prepiercing position against the large hydroforming force in the part acting on the plunger in this plunger position.
The present invention provides for easy and precise adjustment of the positioning of a backup plunger where the plunger is required to be precisely positioned in a certain prepiercing position in order to obtain the desired hydroprepiercing action without premature piercing of the part and with a lowered hydroforming fluid pressure in the part being hydroformed that is less prone to leakage past the plunger. This is accomplished with in-die hydropiercing apparatus that basically comprises a plunger actuating hydraulic cylinder, and a cam device that determines the prepiercing position with a wedge shape cam that is associated with the plunger and is positioned by a cam actuating hydraulic cylinder having a piston rod whose positioning and thus that of the cam and thereby the prepiercing position is easily and finely adjustable. Moreover, the wedge shaped cam is also utilized to resist the force of the high hydroforming pressure acting in the part and on the plunger during both the prepiercing operation and the actual piercing operation thereby relieving the plunger actuating hydraulic cylinder of this task for these operations.
Both the hydroforming position and the prepiercing position of the backup plunger are easily adjustable in one embodiment with separate fined threaded adjusting screw devices associated with the hydraulic cylinders wherein one adjusting screw device is directly associated with the plunger actuating hydraulic cylinder and a cam positioning adjusting screw device is directly associated with the cam actuating hydraulic cylinder. And the wedge shaped cam in this one embodiment is interposed between the backup plunger and the piston rod of the plunger actuating hydraulic cylinder.
In another embodiment, the two hydraulic cylinders are arranged in tandem and the cam is interposed between the piston rods of the two hydraulic cylinders. And only one adjusting screw device that is associated with the cam actuating hydraulic cylinder provides for adjusting and setting the prepiercing position of the backup plunger.
Moreover, in the case where multiple holes are to be pierced in the hydroformed part, the in-die hydropiercing apparatus of the present invention is also adapted so as to minimize the momentary delay between the piercings. And in a further embodiment, the in-die hydropiercing apparatus is both simplified and provides enhanced operation so that in the case of piercing multiple holes, the momentary delay time between piercings is eliminated. As well as the need to provide sealing between the plunger and the die button, thereby reducing the tolerances for the plunger and the die button and thus reducing their cost.
These and other aspects of the invention will become more apparent from the following detailed description of several exemplary embodiments of the present invention shown in the accompanying drawings.